Summary of Work: Apoptosis is a form of programmed cell death that occurs under numerous developmental and physiological conditions. Apoptosis has now been implicated in over 50 human diseases including, cancer, AIDS and autoimmune diseases. Environmental toxins directly activate apoptosis in humans. 1) We are studying the catabolic effectors that are necessary for apoptosis to occur. We have identified and characterized one nuclease which is a member of the cyclophilin family of proteins. We have also shown that 28S ribosomal RNA is specifically degraded during apoptosis. We have shown that cell shrinkage is necessary for the progression of the cell death protein. 2) Apoptosis can be activated by many different signals operating through a diverse array of signal transduction pathways. We have sought to define common activation pathways for apoptosis that are independent of cell type and apoptotic signal. We have shown that cell shrinkage and K+ efflux must occur for caspase activation, ribosomal RNA and DNA fragmentation. Current efforts are directed towards elucidating the ion channels necessary for K+ efflux. 3) A third effort has been in the area of genetic approaches to define novel anti-apoptotic genes. Somatic cell fusion studies have shown that the apoptotic phenotype is recessive and using a rescue cloning approach we have recently cloned several novel inihibitors of apoptosis. 4) We are also identifying the mechanisms of transcriptional activation of apoptosis by glucocorticoids with particular emphasis on kinases/phosphatases whose activity can affect protein phosphorylation. 5) Finally, we are evaluating the role of calcium ions in apoptosis.